Prior art leg adjustment devices are not without their problems being either extremely complicated and, therefore, expensive to build or difficult to use, heavy or limited to specific adjustment lengths.
A search of the prior art did not disclose any patents that read directly on the claims of the present invention or that rendered the present invention obvious or predictable, however, several references, pertaining mainly to adjustment attachments for conventional ladders, were considered related.
U.S. Pat. No. 5,577,574, issued in the name of Joseph. The Joseph patent discloses an adjustable stepladder that incorporates the use of four telescoping legs to allow the user to place the ladder on uneven surfaces. Each adjustable leg employs locking pins held by springs to lock the leg in the desired position, the intent being to allow the user to place the ladder on uneven surfaces. This device, however, suffers from several problems that not only make ineffective in achieving its purpose, but also present inherent dangers to the user. It is obvious from the disclosure that the spacing of the adjustment apertures is far too large to ensure its safe operation. The result of this spacing is such that proper ladder adjustment, in many situations, would be difficult if not impossible to achieve. In the commonly occurring case where the adjustment distance required is slight, adjustment of the ladder legs could result in a more uneven ladder orientation than if it was placed on the surface without adjustment. Also, because of these problems, it will often be the case where the user must select between two or more ladder configurations, each of which presenting an uneven ladder orientation, without being able to determine which, if any, are safe to use. However, there are no provisions in the Joseph disclosure for any devices that would indicate a safe or proper ladder orientation.
Two patents disclose self-leveling ladder constructions for dual-rail type ladder designs: U.S. Pat. No. 4,627,516, issued in the name of Studer, discloses an automatic, self-leveling ladder which adjusts itself and locks to accommodate an uneven surface. The device incorporates coil springs and stub shaft gears which are automatically engaged by the weight of the ladder in order to lock the legs in a level position. U.S. Pat. No. 4,497,390, issued in the name of Wilson, discloses a self-adjusting ladder wherein sliding legs are physically linked to one another by a series of steel balls contained in a flexible tube. The balls transfer the force from one leg of the ladder to the other so that when the bottom of a leg is met with an uneven surface, the ladder will automatically level itself. The Wilson inventions suffers from an obvious problem wherein there is no means by which to lock the legs in position once adjusted to the proper level. This creates an extremely dangerous situation where the shifting of weight upon the ladder would cause the legs to react and possibly result in the ladder tipping over. The Studer invention, while providing a leg locking means, is complex in design will most likely be too expensive to successfully produce. Also, it is apparent from these disclosures that the displacement of the adjustable legs is not sufficient to accommodate a large slope, as would be the case where the user desires to use the ladder on surfaces such as stairs or the like. Furthermore, neither of these disclosures anticipate the use of any devices that would indicate a safe or proper ladder orientation, nor do they address the need to provide leveling capabilities to a stepladder-type device.
Several patents disclose ladder leveling attachments of varying designs for use with dual-rail type ladder designs wherein both legs are fit with telescopically adjustable leg extensions: U.S. Pat. No. 5,669,462, issued in the name of Jennings, discloses an adjustable ladder that incorporates the use of telescoping leg extensions, attaching them to the ladder side rails to allow the user to place the ladder on uneven surfaces. Bolts and wing nuts are used to secure the leg extensions members to each side rail. U.S. Pat. No. 5,542,497, issued in the name of Macyszyn, discloses a ladder level adjusting attachment that incorporates a self-locking cam mechanism, attached to the side rail of the ladder, that locks a telescoping leg extension in place automatically when placed on an uneven surface. U.S. Pat. No. 5,107,958, issued in the name of Johnson, discloses an apparatus consisting of a pair of telescoping leg extension attachments. A threaded screw bolt functions along with a spring pin head to hold the leg extension in position via insertion through a ladder receiving sleeve. U.S. Pat. No. 4,844,208, issued in the name of Veness, discloses an attachment for a ladder whereby a wooden extension is secured to the leg of such ladder to accommodate uneven surfaces. The attachment comprises a metal channel which receives desired length of wood for forming a ladder leg extension. A pair of shafts extend through and between the walls of the metal channel. Pins project from one shaft to engage and retain the wooden extension. A handle, welded to the shaft, actuates the pins to engage and release the wooden extension. U.S. Pat. No. 3,414,082, issued in the name of Gilland, discloses a ladder leveling apparatus intended for use with metal ladders to accommodate uneven surfaces. The telescopic attachment consists of an extension mounting member adapted for pivotal attachment. It incorporates pivot bolts and wing-nuts to be inserted at selected positions. All of these devices are intended for use with dual-rung ladders and do not anticipate use with conventional stepladder designs. Also, it is apparent from many of these disclosures that the displacement of the adjustable legs is not sufficient to accommodate a large slope, as would be the case where the user desires to use the ladder on stairs or the like. In many of these devices, the adjustments are made in increments that may not adequately compensate for the surface slope, resulting in unsafe ladder positioning. Furthermore, none of these disclosures anticipate the use of any indicating devices that would aid the user in determining a safe or proper ladder orientation.
Several patents disclose ladder leveling attachments of varying designs for use with dual-rail type ladder designs wherein one of the legs is fit with a telescopically adjustable leg extension: U.S. Pat. No. 5,064,024, issued in the name of Barham, discloses a vertically adjustable ladder leg extender apparatus for attachment to a single leg of a ladder, extending the leg in order to accommodate uneven surfaces. The device consists of a sleeve that carries an extendible support leg which slides vertically therein. The support leg is vertically adjustable and secured in place by turn bolts. U.S. Pat. No. 5,027,923, issued in the name of Derome, discloses an attachment for a ladder which includes a housing with an extensible leg to allow use on an uneven surface. A locking mechanism is mounted in the housing and consists of a cam having a lobe which engages the extensible leg. The extensible leg is moved downward by an attached foot-step. A release lever is attached for retraction into the housing. The top of the housing has a bubble level to determine when ladder is level with respect to the direction of the ladder rungs. U.S. Pat. No. 4,802,471, issued in the name of Cordell, discloses an attachment for a ladder to accommodate uneven surfaces. The attachment consists of a T-shaped gripping device with a sharp edge that makes contact with a smooth slidable rail, locking the rail into the desired position. The slidable rail extends the ladder leg, thus leveling it. Pressure is applied to the gripping device to remove contact between it and the smooth rail thus allowing the rail to have an infinite number of positions being limited only by the length of such smooth rail. An infinite number of positions are possible because a smooth surface is utilized rather than ratchets. U.S. Pat. No. 4,766,976, issued in the name of Wallick, Jr., discloses an attachment for a ladder to accommodate uneven surfaces. The apparatus provides a ladder leg extender and leveler consisting of a longitudinally extending frame structure that is attached, in a face-to-face relation to a ladder leg side. The apparatus avoids undesirable bending stresses that have formerly been placed on the rung fasteners by employing a base leg recess. The apparatus incorporates a hollow longitudinal extension leg which slides through apertures and a ball and socket arrangement to level the ladder. The apparatus further employs a number of stacked annular clamp plates and a helical spring to lock the extension leg in the desired position. U.S. Pat. No. 5,615,752, issued in the name of Wassil, discloses a ladder-leveling platform assembly in which such platform can be adjusted to accommodate an uneven surface. The assembly consists of a base with a pivotable plate that is supported on a platform. Elevation is accomplished by the use of rods that are used to maintain a plate which is joined to an axle along with a series of apertures inclined to elevate the ladder leg to a desired position. The plate receives one ladder leg. None of these leveling devices can be used in conjunction with a conventional stepladder design due to the fact that they all are intended to be placed on a single leg of a dual-rail type ladder design. Since stepladders have four legs, use of these devices would result in extremely unstable ladder positioning, creating the potential for injury. Also, it is apparent from many of these disclosures that the displacement of the adjustable legs is not sufficient to accommodate a large slope, as would be the case where the user desires to use the ladder on stairs or the like. In many of these devices, the adjustments are made in increments that may not adequately compensate for the surface slope, resulting in unsafe ladder positioning. Although the Derome device anticipates the use of a bubble level to indicate proper position indication, it fails to take into consideration the fact that a stepladder requires two-dimensional leveling, both parallel and perpendicular to the ladder rungs.
U.S. Pat. No. 6,779,632 to Parks, III, discloses another leg adjustment device using bolts that extend through a dual-rail design. This design would require tools to adjust the length of the legs, have parts that could be lost and take unnecessary time to adjust causing users to not adjust the legs and endanger themselves by, for example, over reaching.
U.S. Pat. No. 6,595,326 to Dean discloses a very complicated device for adjusting the length of ladder legs. In addition to being overly complicated the device is limited to specific adjustment lengths.
U.S. Pat. No. 6,401,866 to Roy discloses a complicated ratchet-type device for adjusting the legs of ladders. Such devices are expensive to make and also are limited to specific adjustment lengths.
U.S. Pat. No. 5,526,898 to Clark discloses a leg extension assembly that uses a dual-rail system wherein the lower rail is raised and lowered by a turn screw. This device suffers from being overly complicated and difficult and time consuming to use.
What is needed is a leg adjustment device for use in ladders and the like that is inexpensive to make, easy to use and permits the adjustment of the leg member to any position within the lower and upper limits of the adjustment range.